<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>

    <div class="ttqwe"></div>
    <script>

        // var div = document.querySelector("div")
        // function addClass(el, className) {
        //     el.classList.contains(className) ? "" : el.className += " " + className
        // }

        // addClass(div, "qwe")

    </script>
</body>

</html>